Fluoride in coral aragonite related to seawater carbonate

KENTARO TANAKA, SHIGERU OHDE
2010 Geochemical Journal  
fluoride content in carbonate and its incorporating process were investigated for natural and inorganic calcium carbonate. Carpenter (1969) measured the fluoride content in marine carbonates such as corals, foraminifera and coccoliths, and found that coral aragonite has a higher concentration than calcite skeletons (foraminifera and coccoliths). Kitano and Okumura (1973) performed carbonate synthesis experiments using a Ca 2+ -HCO 3 --Mg 2+ -Fsolution and found that the amount of fluoride
more » ... t of fluoride incorporated into aragonite is larger than that into calcite, but the mechanism of incorporation was not elucidated. Rosenthal and Boyle (1993) and Rosenthal et al. (1997) measured the fluoride content of foraminiferal shells (aragonite and calcite), and pointed out that the fluoride coprecipitation was primarily controlled by the biological processes, since the fluoride content has little correlation with seawater temperature. Using SIMS, Hart and Cohen (1996) measured Sr/Ca and F/Ca ratios along the growth axis of a coral skeleton. They reported that the variation of Sr/Ca and F/Ca ratios has a one-year cycle. Ichikuni (1979) performed a significant research on the coprecipitation experiments of fluoride with aragonite using a CaCl 2 -Na 2 CO 3 -NaF solution. He demonstrated that the uptake of fluoride by aragonite is attributed to the ion-exchange reaction, in which one carbonate ion in aragonite is replaced by two fluoride ions. The ion-exchange reaction can be represented as follows: CaCO 3(s) + 2F - CaF 2(s) + CO 3 2- (1) Fluoride in coral aragonite related to seawater carbonate
doi:10.2343/geochemj.1.0079 fatcat:hxlprfmsr5f77btco2nla2l2ca